LEASES LEASES - LEASE COST (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) Rate	Jun. 30, 2019 USD ($) Rate
Lessee, Lease, Description [Line Items]
Operating Lease, Expense	$ 148	$ 318
Sublease Income	(3)	(6)
Lease, Cost	$ 145	$ 312
Aircraft [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.20%	4.20%
Operating Lease, Cost	$ 62	$ 123
Operating Lease, Weighted Average Remaining Lease Term	6 years 9 months 18 days	6 years 9 months 18 days
CPA Aircraft [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.30%	4.30%
Operating Lease, Cost	$ 20	$ 40
Operating Lease, Weighted Average Remaining Lease Term	9 years 8 months 12 days	9 years 8 months 12 days
Airport Facilities [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.10%	4.10%
Operating Lease, Cost	$ 62	$ 146
Operating Lease, Weighted Average Remaining Lease Term	10 years 4 months 24 days	10 years 4 months 24 days
Corporate real estate [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.40%	4.40%
Operating Lease, Cost	$ 4	$ 9
Operating Lease, Weighted Average Remaining Lease Term	37 years 8 months 12 days	37 years 8 months 12 days